To meet the demands for ultra-precision positioning and micro machining systems, hydrostatic bearings with very small friction have become an indispensible key component for high precision machine tools. With the excellent stiffness, damping capacity, chattering suppression capability during cutting processes, and micron (nanometer) order high precision positioning capability, the hydrostatic bearings can provide a good solution to the bearing design for ultra-precision cutting machine tools. Therefore, the hydrostatic bearings are utilized in the bearing system of the guide rail of almost all the high-level precision machine tools around the world.
In existing linear slide tables that employ the hydrostatic bearing, pressurized lubricant oil is conveyed through a flow restrictor (or compensator) to an oil recessed chamber between a slide rail and a loading table to form a supporting oil film separating two metal contact surfaces apart thus achieving a liquid friction. The ideal value for the thickness of the initial oil film between the slide rail and the loading table can be known through theoretical analysis and calculation. The linear slide tables employing the hydrostatic bearing currently adopt two methods to achieve the ideal initial oil film thickness. One method is to employ a grinding process, i.e., according to the size of an existing slide rail, a grinding process is used to process the surface of loading table that can achieve the ideal thickness of the initial oil film. The other method is to use screw adjustment. For example, in a clearance adjustment apparatus as disclosed by Republic of China (Taiwan) patent publication no. 435628, the clearance between each bearing and the matching surface of the slide rail is individually adjusted through screws to achieve the ideal thickness of the initial oil film.
However, the fabrication cost of the linear slide table employing the grinding process is very high. In addition, if the slide rail surface experiences a frictional wear after in service for a period of time, the oil film thickness cannot be readjusted and the linear slide table must be replaced with a new one. On the other hand, in the linear slide table using the screw adjustment, the clearance between each bearing and the slide rail needs to be individually adjusted at the same time. Therefore, it is very difficult to obtain a uniform oil film thickness by adjusting all screws equally thus this may affect the overall performance and reliability of the linear slide table.